This invention relates to waveguide switching apparatus, and more particularly to switching apparatus used in high power microwave energy arrangements.
A simple known waveguide switch, which may be termed an "S" switch, is illustrated in FIG. 1, which is a transverse section through the stator and rotor of a switch, and FIG. 2, which is a longitudinal section through the rotor and bearings. The switch comprises the rotor 1, which is generally cylindrical in form, and which is arranged to rotate on bearings 2 in the stator 3. Four waveguide channels 4, 5, 6 and 7 are located within the stator 3 and provide passages along which microwave energy may be transmitted. Each of the waveguide channels 4, 5, 6 and 7 terminates at a port A, B, C and D respectively, which is arranged adjacent to the rotor 1, the ports A, B, C, D lying in the same plane and being arranged at 90.degree. intervals around the rotor 1. The rotor 1 includes two curved passages 8 and 9 located within it which are arranged such that their openings at the rotor surface are spaced at 90.degree. intervals. In the orientation shown in FIG. 1, no interconnections are made between the ports A, B, C and D in the stator 3. However, if the rotor 1 is rotated through 45.degree. in a clockwise direction, ports A and B, and ports C and D become interconnected. If the rotor 1 were to be rotated anti-clockwise through 45.degree. from the illustrated position, then ports A and D would be interconnected, and ports B and C interconnected. Thus, for example, energy transmitted along waveguide channel 4 may be switched into channel 5 or channel 7 depending on the orientation of the rotor 1.
An arrangement in which "S" switches are used is illustrated in FIG. 3, which is a schematic diagram of an amplifying stage employed in a satellite. The arrangement comprises five amplifiers 10, 11, 12, 13 and 14, which are arranged to amplify high power microwave signals applied to them on input lines 15, 16, 17, 18 and 19. Two spare amplifiers, 20 and 21, are also included in the arrangement. A plurality of "S" switches 22 are included and are arranged so that, if one of the amplifiers 10 to 14 fails, one of the spare amplifiers 20 and 21 may be switched into the circuit in its place. As can be seen, a large number of "S" switches, in this case twenty, are required to ensure that a failure in any two of the five amplifiers 10 to 14 can be compensated for by switching in the spare amplifiers 20 and 21. Failure of any two amplifiers in this configuration will require the operation of four switches to switch in the two spare amplifiers. For example, if a failure were to occur in amplifier 12, then switches 23 and 24 must be rotated through 90.degree. to switch the applied signal on line 17 through the spare amplifier 20. If another failure occurs, for example, if the amplifier 13 were to fail, then the rotors of switches 25 and 26 must be rotated through 90.degree. to switch the signal on line 18 to the spare amplifier 21.
Another type of waveguide switch, which may be termed an "R" switch, is illustrated in FIG. 4, which is a transverse section through the stator and rotor of such a switch, and FIG. 5, which is a longitudinal section through the rotor and bearings. The "R" switch is similar to the "S" switch described with reference to FIGS. 1 and 2, in that it includes two curved passages 27 and 28 within the rotor 29. In addition, the rotor 29 also includes a further passage 30, which is straight and is arranged between the curved passages 27 and 28, along a diameter of the rotor 29. This configuration permits a larger variety of interconnections to be made between four waveguide channels 31, 32, 33 and 34 located within the stator 35, and having ports A, B, C and D respectively, than is possible with an "S" type switch. In the position illustrated in FIG. 4, ports B and D only are interconnected. If the rotor 29 is rotated through 45.degree. clockwise from the position shown, then ports A and B are interconnected, and ports C and D interconnected, by the curved passages 27 and 28 respectively. Similarly, ports B and C may be connected, and ports A and D, if the rotor is rotated through 45.degree. anti-clockwise from the illustrated position. Therefore, in a particular arrangement, fewer switches may need to be included if they are "R" type switches rather than "S" type switches. However, although an arrangement using "R" switches may include fewer switches, a greater number of switching operations tend to be necessary if failure occurs. The essential reliability of the switches depends on the number of switching operations which are required to effect a desired path change and it is desirable, therefore, especially in applications where failure cannot easily be rectified, that a minimum number of switching operations are employed.
Another waveguide switch, which may be termed a "T" switch, is illustrated in FIGS. 6 and 7, which are transverse and longitudinal sections respectively through the rotor 36 of such a switch. The "T" switch is similar to the "R" switch, in that it includes two curved passages 37 and 38 through the rotor and a straight passage 39 across a diameter of the rotor. In addition, another passage is also included to provide a connection orthogonal to that provided by the straight passage 39. The additional passage is a cross-under passage 40 which has ports in the same plane as the other passages in the rotor 36, but which passes underneath them, as shown in FIG. 7. This type of switch enables a greater variety of interconnections to be made than does either an "S" or an "R" switch. Thus, where "T" switches are included, in an amplifying section for example similar to that shown in FIG. 3, the same number of switches are required as would be necessary if "R" switches were to be used and the number of switching operations necessary to include spare amplifiers in the circuit is the same as in an arrangement which uses "S" type switches. However, a "T" type switch is much larger than either an "S" or "R" type switch having similar sized channels, and requires a thicker rotor of larger diameter to accommodate the four passages. This increases the inertia of the rotor considerably, which has the disadvantage that switching accuracy may be reduced and greater torque is required for the switch to be operated. Also heating effects associated with the "T" switch dictate that a large spacing be left between the rotor and stator to allow for expansion. This may result in an unacceptable degree of leakage where the waveguide channels feed into the passages in the rotor.